Unknown modifier '(' when using preg_match() with a REGEX expression [duplicate] - php

Question

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Warning: preg_replace(): Unknown modifier
(3 answers)
Closed 3 years ago.
I'm trying to validate dates like DD/MM/YYYY with PHP using preg_match(). This is what my REGEX expression looks like:
$pattern = "/^([123]0|[012][1-9]|31)/(0[1-9]|1[012])/(19[0-9]{2}|2[0-9]{3})$/";
But using it with a correct value, I get this message:
preg_match(): Unknown modifier '('
Complete code:
$pattern = "/^([123]0|[012][1-9]|31)/(0[1-9]|1[012])/(19[0-9]{2}|2[0-9]{3})$/";
$date = "01/03/2011";
if(preg_match($pattern, $date)) return TRUE;
Thank you in advance

Answer 1

Escape the / characters inside the expression as \/.
$pattern = "/^([123]0|[012][1-9]|31)\/(0[1-9]|1[012])\/(19[0-9]{2}|2[0-9]{3})$/";
As other answers have noted, it looks better to use another delimiter that isn't used in the expression, such as ~ to avoid the 'leaning toothpicks' effect that makes it harder to read.

Answer 2

You use / as delimiter and also in your expression. Now
/^([123]0|[012][1-9]|31)/
Is the "complete" expression and all following is expected as modifier, also the (.
You can simply use another delimiter.
~^([123]0|[012][1-9]|31)/(0[1-9]|1[012])/(19[0-9]{2}|2[0-9]{3})$~
Or you escape all occurence of / within the expression, but I would prefer another delimiter ;) Its more readable.

Answer 3

your delimiter is /, but you are using it inside the pattern itself.
Use a different delimiter, or escape the /

Answer 4

You could escape the slashes / as suggested. It'll eventually lead to the Leaning Toothpick Syndome, though.
It's common to use different delimiters to keep your regular expression clean:
// Using "=" as delimiter
preg_match('=^ ... / ... $=', $input);

Answer 5

checek date using below function
function checkDateFormat($date)
{
//match the format of the date
if (preg_match ("/^([0-9]{2}) \/([0-9]{2})\/([0-9]{4})$/", $date, $parts))
{
//check weather the date is valid of not
if(checkdate($parts[2],$parts[1],$parts[3]))
return true;
else
return false;
}
else
return false;
}
echo checkDateFormat("29/02/2008"); //return true
echo checkDateFormat("29/02/2007"); //return false